deck 1 (dĕk) n. 1. A platform extending horizontally from one side of a ship to the other. 2. a. A platform or surface likened to a ship's deck. b. An unroofed platform, typically with a railing, that adjoins a building or is built on a rooftop. c. The roadway of a bridge or an elevated freeway. 3. The piece of hard material, usually wood or composite ...